Self-depressing underwater towable spread

ABSTRACT

1. An underwater towable spread adapted to ride through a seaway at a predetermined depth when towed at a selected speed comprising in combination, A NON-BUOYANT TOW CABLE HAVING A DISTAL END AND A BUOYANT TOWABLE ASSEMBLY CONNECTED AT ITS FORWARD END TO THE DISTAL END OF SAID CABLE, SAID ASSEMBLY CONSISTING OF AN ELONGATED NON-BUOYANT INSTRUMENTALITY HAVING A LONGITUDINAL AXIS, AN ELONGATED FLOAT MEMBER STREAMLINED FOR MOTION ALONG ITS LONGITUDINAL AXIS, MEANS RIGIDLY SECURING SAID FLOAT MEMBER TO SAID INSTRUMENTALITY IN LATERALLY SPACED RELATION AND WITH THEIR RESPECTIVE AXES SUBSTANTIALLY PARALLEL, SAID ASSEMBLY BEING CONSTRUCTED AND PROPORTIONED SO THAT WHILE THE SPREAD IS AT REST, THE ASSEMBLY FLOATS AT THE WATER SURFACE, ITS CENTER OF GRAVITY IS SPACED BELOW AND FORWARD OF ITS CENTER OF BUOYANCY WITH RESPECT TO SAID AXES AND AFT OF SAID TOW CONNECTION THEREBY GIVING ROLL STABILITY AND A STATIC TRIM BY THE HEAD, AND WHILE THE SPREAD IS TOWED AT THE SELECTED SPEED THE ASSEMBLY SUBMERGES TO RIDE AT THE PREDETERMINED DEPTH.

iJnited States Patent [191 Kelly Nov. 25, 1975 sELF-DEPREssING UNDERWATER TOWABLE SPREAD [75] Inventor: Raymond E. Kelly, Panama City,

Fla.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, D.C.

[22] Filed: Oct. 10, 1962 [21] Appl. No.: 230,032

Primary ExaminerVerlin R. Pendegrass Assistant Examiner-Harold Tudor Attorney, Agent, or FirmLouis A. Miller; Rolla N. Carter EXEMPLARY CLAIM 1. An underwater towable spread adapted to ride through a seaway at a predetermined depth when towed at a selected speed comprising in combination,

a non-buoyant tow cable having a distal end and a buoyant towable assembly connected at its forward end to the distal end of said cable, said assembly consisting of an elongated non-buoyant instrumentality having a longitudinal axis,

an elongated float member streamlined for motion along its longitudinal axis, means rigidly securing said float member to said instrumentality in laterally spaced relation and with their respective axes substantially parallel, said assembly being constructed and proportioned so that while the spread is at rest, the assembly floats at the water surface, its center of gravity is spaced below and forward of its center of buoyancy with respect to said axes and aft of said tow connection thereby giving roll stability and a static trim by the head, and while the spread is towed at the selected speed the assembly submerges to ride at the predetermined depth.

1 Claim, 3 Drawing Figures 11S. Patnt Nov; 25, 1975 3,921,562

10 AT REST 13 1 18 UNDER TOW FIG. 2

INVENTOR. Raymond E. Kelly SELF-DEPRESSING UNDERWATER TOWABLE SPREAD The invention described herein may be manufactured and used by and for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to an underwater towable spread adapted to ride through a seaway at a predetermined depth when towed at a selected speed and more particularly to such a spread which has low drag and can be towed at high speeds (greater than 20 knots) with good stability.

It is desirable to tow passive or active instrumentalities, such as a noisemaker for sweeping acoustic mines, at a given depth through a body of water. Typical of towing arrangements presently in use is to provide the trailing end of the spread with a surface riding float and a weight or depressor for maintaining the end of the spread at the desired depth. Such arrangements add greatly to the drag of the spread and at best are bulky as well as cumbersome to stream, recover and stow. Of

greater importance, however, is that such arrangements have been found to be unstable at high towing speeds, say speeds greater than 20 knots. Accordingly, an object of the present invention is to provide a towable spread of low drag and which at rest in the water supports the instrumentality at the surface and which when under tow at a selected speed depresses itself to ride stably at a predetermined depth.

Another object of the invention is to provide a towable spread which is relatively simple to stream, retrieve and stow.

In accordance with the invention, the towable spread is constructed and proportioned so as to provide buoyancy in the at rest condition sufficient to support at the surface the device to be towed and the distal end of the non-buoyant towing cable. The center of gravity and the tow point are so arranged that in the static condition the device is trimmed to bow-down attitude i.e., trimmed by the head. More specifically, the center of buoyancy is displaced vertically and aft of the center of gravity of the device itself. As the tow vessel gets under way, the device, due to its bow-down attitude, presents a lifting surface (downward) to the stream which results in sufficient dynamic force to overcome the buoyancy and cause the device to submerge, initially to a .depth greater than the desired depth of tow. However, as the speed of tow increases to the preselected speed,

the drag of the heavy tow cable increases to bring the resulting force of the tow cable on the device to more nearly horizontal, resulting in a force (moment) which causes the attitude of the device to assume a low angle with the horizontal such that the vertical forces on the device are more nearly balanced and the depth of tow obtained is largely determined by the size, weight, and length of the submerged section of the tow cable. In order to minimize drag and provide the desired lifting forces, the device as a whole when unitary, or its individual parts, is streamlined for motion along its longitudinal axis to the extent feasible, the exact shape being very much dictated by the technical function of the device. This is the same limitation that is encountered in designing engine nacelles and the like for aircraft.

If it is known that the device or instrumentality is to be towed at a single depth and at a unique speed, it can,

of course, be built originally as a single structure incorporating the foregoing design characteristics. Frequently it is desirable to obtain the advantages of the invention for devices or instrumentalities originally designed to be towed while supported by a surface float (with or without a depressor) in which cases the buoyancy and trim of the tow device can more readily be provided by rigidly attaching to the device a suitable streamlined buoyant member adapted to submerge along with the towed device, it being recognized that such towed devices were initially designed and shaped to reduce their drag through the water and thus may be considered streamlined. The embodiment of the invention to be described in detail is in the latter category of modifying an existing device.

The invention itself, as well as other objects and advantages thereof, will become clear from the following description when read in connection with the accompanying drawing wherein FIGS. 1 and 2 are diagrammatic side views, respectively, of a design incorporating the invention in its at rest and under tow positions in a body of water; and

FIG. 3 is a view in perspective of the device diagrammatically shown in FIGS. 1 and 2.

As illustrated in the drawing, the assembly consists of a streamlined float member 10 rigidly secured above a nonbuoyant venturi device 11 adapted to be towed through a seaway by a tow cable 12 connected to a towing bail l3 rigidly secured to the venturi device 11 in any suitable manner as by rivets 14. The rigid connection between the float member 10 and the venturi device 11 is preferably made adjustable so that the angle in the vertical plane between the longitudinal axis of the float member 10 and the longitudinal axis of the venturi device 11 may be altered to stabilize the towing characteristics of the assembly. The adjustable connections shown comprises a pivotal linkage 15 near the forward end of the assembly and extendable plate members 16 rearwardly thereof which are held in the adjusted position by bolts 17. A vertically dependent tail fin 18 secured to the bottom side of the float member 10 serves to minimize roll and otherwise stabilizes the towing properties of the assembly. Additional roll stability is contributed by the vertical displacement between the center of buoyancy and the center of gravity. Elevator fins 19 secured to the tail fin 18 aid in controlling the running depth of the assembly when under tow and the angle of attack of the fins 19 with respect to the center line of the float member 10 is preferably made adjustable to regulate or alter the running depth. As shown in FIG. 3 the elevator fins 19 are pivotally mounted on a rod 21 carried by the tail fin l8 and adapted to be secured in various angular positions by means of a bolt 22 extending through a lug 23 integral with the fins l9 and an arcuate slot 24 in the tail fin 18. As was pointed out above, the venturi device 1 1 may be provided with a faired depending casing for housing an electric motor 25 or other mechanism but inasmuch as such mechanism forms no part of the present invention it is not herein described.

Inasmuch as the above towable spread does not readily lend itself to precise mathematical analysis, it may help others to practice the invention, perhaps empirically, if the present embodiment illustrated is described in quantitative terms. In this embodiment the venturi device 11 is 3% feet in length, its maximum diameter is approximately 13 inches, its weight in seawater 129 pounds and its center of gravity substantially as illustrated in FIGS. 1 and 2. The streamlined float member is 5 feet in length, its maximum diameter is inches, its center of buoyancy approximately as indicated in FIG. 1, which center of buoyancy is displaced vertically 15 inches and aft 1 inch with respect to the center of gravity of the venturi device 11, and its buoyancy such that when submerged with the venturi device 11 the assembly has a resultant positive buoyancy of 50 pounds. The tow point at the forward end of the rigid bail 13 is 2% feet forward of the front end of the venturi device 11. When towed at a speed of approximately 26 knots with a tow cable of 0.88 inch diameter and a weight of 0.11 pounds per lineal foot in sea water and a towing scope of 850 feet the assembly towed with good stability at a depth of 18 feet when the elevator fin 19 was adjusted to a 5 up angle. It might be added that the longitudinal axes of the float l0 and the venturi device 11 were parallel, the towing tension was 2600 pounds, and the attitude of the assembly was 4.5 bowdown.

It will be appreciated from the foregoing that the towable spread incorporating the invention will in its static condition support the distal end of the tow cable at the water surface and thus tend to keep the cable off the bottom and prevent loss of the device; in addition, the resistance of the tow cable spread to motion through the water is relatively low.

While for the purpose of disclosing the invention, a specific operative embodiment thereof has been de- 4 scribed in detail, it will be evident to those skilled in the art that the invention is not limited thereto, but may take other forms within the intended scope of the appended claims.

What is claimed is:

1. An underwater towable spread adapted to ride through a seaway at a predetermined depth when towed at a selected speed comprising in combination,

a non-buoyant tow cable having a distal end and a buoyant towable assembly connected at its forward end to the distal end of said cable,

said assembly consisting of an elongated non-buoyant instrumentality having a longitudinal axis, an elongated float member streamlined for motion along its longitudinal axis, means rigidly securing said float member to said instrumentality in laterally spaced relation and with their respective axes substantially parallel, said assembly being constructed and proportioned so that while the spread is at rest, the assembly floats at the water surface, its center of gravity is spaced below and forward of its center of buoyancy with respect to said axes and aft of said tow connection thereby giving roll stability and a static trim by the head, and while the spread is towed at the selected speed the assembly submerges to ride at the predetermined depth. 

1. An underwater towable spread adapted to ride through a seaway at a predetermined depth when towed at a selected speed comprising in combination, a non-buoyant tow cable having a distal end and a buoyant towable assembly connected at its forward end to the distal end of said cable, said assembly consisting of an elongated non-buoyant instrumentality having a longitudinal axis, an elongated float member streamlined for motion along its longitudinal axis, means rigidly securing said float member to said instrumentality in laterally spaced relation and with their respective axes substantially parallel, said assembly being constructed and proportioned so that while the spread is at rest, the assembly floats at the water surface, its center of gravity is spaced below and forward of its center of buoyancy with respect to said axes and aft of said tow connection thereby giving roll stability and a static trim by the head, and while the spread is towed at the selected speed the assembly submerges to ride at the predetermined depth. 